DURABILITY CHARACTERISTICS OF PORTLAND CEMENT/VOLCANIC ASH CONCRETE EXPOSED TO CHEMICALLY AGGRESSIVE ENVIRONMENTS

Current trend in concrete research is towards finding materials that can partially or fully replace cement. However, too much emphasis is given to compressive strength as the quality index; with little or no consideration given to durability property. The concrete can be strong but not durable especially when it is subjected to chemical aggressive environments. This research therefore assessed the durability characteristics of Portland/cement volcanic ash concrete exposed to chemically aggressive environments. Preliminary tests of the different properties of materials used for this research were carried out. The concrete samples were prepared using 5% and 10% volcanic ash replacements and nominal mix of 1:2:4 with a 0.5 w/c ratio. Cube mould of size 100mm x 100mm x100mm and cylinder mould of size 200mm x 100mm were used to cast a total of 405 concrete samples. Out of the 405 samples, 162 cubes were used to assess compressive strength test while 162 cylinders were used to determine the tensile strength by the split tensile method. The specimens were cured in H2O, MgSO4 and H2SO4 and tested at 7, 14, 21, 28, 56 and 90 days. Another set of 81 concrete cube samples were also produced and cured in the same curing media for test on abrasion resistance and water absorption test at 28, 56 and 90 days of age. The results show increase in compressive strength of about 8.68% for concrete samples with 10% volcanic ash replacements than 0% replacements cured in normal environment (H2O) at 28 days. A decrease in compressive strength of about 15.02% was observed for concrete samples with 0% volcanic ash replacements than 10% replacements cured in MgSO4 at 28 days. Also concrete samples with 0% volcanic ash replacements cured in H2SO4 withstood the medium better than the samples with 10% volcanic ash replacements as indicated by 12.78% increase in compressive strength at 28 days. Concrete samples made with 10% volcanic ash replacements have high resistance to abrasion and less sorptivity than 0% volcanic ash replacements in both normal and chemically aggressive environments at 90 days. In conclusion Miango JP 3 is a pozzolanic material having satisfied the requirement of ASTM C618-05. Therefore it was recommended to be used to produce a strong, dense and durable concrete which can be used both in normal and chemically aggressive environments.

1.1                                                         Background of the Study

Concrete was first used as a structural material during the nineteenth century when Portland cement was discovered in Portland England (Yasin et al., 2012). According to Lappiatt and Ahmad (2004) in Shoubi et al.,(2013) it was estimated that the concrete industries throughout the world produces annually about 12 billion tons of concrete and uses about 1.6 billion tons of Portland cement. Thus on average, approximately 1 ton of concrete is produced each year for every human being in the world. Harley (2007) noted that the amount of concrete used in construction industries around the world is more than double that of the total of all other building materials, including wood, steel, plastic and aluminium. For this reason, concrete is the most widely used construction material and it is the second only to water as the most utilized substance all over the world. It has become most widely used due to the availability of its constituents, flexibility, strength, durability, impermeability etc. As a composite material it is commonly used in the construction of buildings and infrastructures. Merrit and Ricketts (2001) defined concrete as a mixture of Portland cement or any other hydraulic cement, fine aggregate, coarse aggregate and water, with or without admixtures.